1. Field of Invention
This invention relates to the balancing of a rotating assembly having radial projections such that the vibratory effect of having the center of rotating mass eccentric to the axis of rotation is minimized.
2. Related Art
Whether used for aerodynamic lift, for the generation of power, or for cooling, the radial projections, or air foils in these cases, are part of a rotating assembly. It is necessary that the center of mass of the rotating assembles is concentric with its axis of rotation for optimal performance of these respective functions. Any deviation from this concentricity will represent additional forces which must be borne by a given structure that supports the rotating assembly. These additional forces manifest themselves as vibration and can not only interfere or diminish the ability of the rotating object to perform its function but can also accelerate the fatigue life of all the interconnected components themselves e.g. bearings, gears, shafts, structural supports connected to the rotating assembly. In wind or water turbines, increasing the degree of unbalance not only decreases the mechanical life of connected components but will also increase the necessary wind or water velocity required to for the generation of power.
Investigation into related art shows several methods to statically balance detached blades. Referenced in U.S. Pat. No. 5,824,897 to Beachum et al. (1998) and taught in U.S. Pat. No. 4,991,437 to Hanchett (1991) is a method to have a specimen blade connected to a reference blade over a fixed fulcrum where the fulcrum is positioned at the point of connection between the two blades. Corrective weight is either added or subtracted in a trial and error method until the respective blades are in equilibrium with each other. That is to say, if the blades are positioned in a horizontal fashion and released, the blades will remain stationary or balanced. The size of the fulcrum assembly would be proportional to the size of the blade being balanced. On large wind turbine blades whose length can be in excess of 60 meters and whose weight can be in excess of 16,000 kg, the fixture size would render it non-portable. Additionally, the area to balance the blades would be in excess of twice the blade length. Furthermore, a trial and error method is less efficient with respect to time as compared with having a prescriptive weight and distance correction. It would be impractical to establish a profile of weight distribution or span wise and chord wise moments for a radial projection. The method and apparatus does not lend itself to any type of automation.
U.S. Pat. No. 5,824,897 to Beachum et al. (1998) discloses a fixture where a single blade is attached to the fixture at its point of attachment and multiple load cells are used to indicate weight. The moment of the blade is then calculated based on the measurement indication of the load cells and the relative distances to the point of attachment. Corrective weight then can be added or subtracted based upon a virtual master blade specification. The fixture is limited to the application of helicopter blades which are of relatively short length as compared to a blade of a wind turbine whose length may exceed 60 meters. Multiple fixtures would be required to service blades from multiple applications. The fixture would necessarily be proportionate to the size of the blade being balanced, rendering the fixture to be non-portable and subsequently not suitable for field use in the extreme case of blades associated with wind turbines. Additionally, it would be impractical to establish a profile of weight distribution or span wise and chord wise moments for a radial projection. The method and apparatus does not lend itself to any type of automation.
It is well known in the art to balance a rotating mass with radial projections as a complete assembly. The art is generally limited to rotating masses which are sufficiently small in diameter, have sufficient speed, and can be performed without external forces such as those which are environmentally induced. U.S. Pat. No. 5,140,856 to Larson (1992) teaches one method of a balancing a complete assembly whose parameters fall outside of the well known art which requires the use of fixtures, specialized equipment and associated skill set, and requires personnel to perform the process at great heights and in proximity to rotating equipment. The method is time consuming and also extremely subject to environmental influences such as wind which will thereby affect the accuracy of the results.
U.S. Pat. No. 7,370,529 to Lenz (2008) discloses a method of balancing a rotating object with radial projections as a complete assembly but is limited to objects where the radial projections rotate around a stationary center. This method only covers a limited class of objects and certainly does not include the class of objects associated with helicopters and wind turbines.
It is desirable to have an improved method and apparatus to balance radial projections that provides a simple, practical, portable, prescriptive, and economical means which not only encompasses the class of radial projections addressed in prior art but is also not restricted to the length of the radial projection as in the extreme case of wind turbine blades. It is also desirable to have a method and apparatus which can allow minimal human intervention during the process as can be realize through process automation.